package 牛客网_N.动态规划.climbing_stairs_5;
/**
 * 递归
 */
import java.util.Scanner;

public class Main {
	public static void main(String[] args){
		Scanner in = new Scanner(System.in);
		int n = in.nextInt();
		
		System.out.println(climbStairs(n));
	}
	
	public static int climbStairs(int n){
		if(n == 1) return 1;
		if(n == 2) return 2;
		return climbStairs(n-1)+climbStairs(n-2);
	}
}
